Cooling of combustor walls is typically achieved by directing cooling air through holes in the combustor walls to provide effusion and/or film cooling. Holes formed in a pre-determined pattern directly through a sheet metal liner of the combustor walls allowing pressurized cooling air to enter the combustion chamber and thereby cool the combustor.
The effusion holes in the combustor walls are typically produced using a laser drilling system. During laser drilling, a laser head and a workpiece are typically moved relative to the each other on a manipulation system such as a computer numerical control (CNC) motion system in order to drill each individual hole. In order to achieve optimum cooling within the combustor, a non-uniform hole pattern is often required. Accordingly, a hole pattern designed for optimum effectiveness may comprise variations in hole density, which results in a hole pattern definition that is often complex. This in turn requires a significant amount of time to set up the laser drilling system, as positional data for each individual hole must be defined and supplied to the CNC motion system.
Current methods of defining complex hole patterns require that the drilling of the effusion holes be done in two stages, wherein a coarser base hole pattern is first drilled, and then, one or more finely-spaced holes are drilled between the base holes to define areas with a higher hole density where additional cooling is required. This requires unnecessary and time-consuming repositioning moves by the laser drilling system which add to the cost of manufacturing the parts. There is thus a need for an improved method of drilling the effusion holes which minimizes manufacturing costs of effusion cooled parts.